Purpose:
Previous studies have demonstrated the uptake and distribution of lysozyme in hydrogel contact lens (CL) materials using the traditional vial incubation method. The purpose of this study was to qualitatively assess the asymmetric uptake of lysozyme by different CL materials using a confocal laser scanning microscopy (CLSM) technique.

Methods:
Six hydrogel CL materials belonging to various FDA groups (group I: polymacon; group II: omafilcon A, nesofilcon A, nelfilcon A; group IV: etafilcon A with Polyvinylpyrrolidone, ocufilcon B) were incubated in an artificial tear solution comprising fluorescently-labelled lysozyme for 16 h at 37°C. Appropriate controls were included. During the incubation, a novel asymmetric condition of lens exposure to ATS was simulated by blocking the posterior surface of the CL with a custom made Teflon® mount. After incubation, the central 5 mm of each CL was punched out and mounted on a microscope slide. The uptake of lysozyme by different CL materials was evaluated using CLSM with argon laser at 488nm.CLs were optically sectioned every 2 µm intervals (z stack). The fluorescence intensity profile of each CL sample was calculated with ImageJ software, using the “Plot Z axis profile” module. The data were normalized to plot the relative fluorescence for each CL profile.

Results:
Mapping of asymmetric lysozyme distribution revealed different patterns of lysozyme penetration into the CLs. All CLs demonstrated the uptake of fluorescently-labelled lysozyme. Polymacon (FDA group I) revealed a relatively higher concentration of lysozyme within the bulk, while the group II materials showed a homogeneous distribution of lysozyme from the anterior to posterior surface. For the group IV materials, lysozyme was deposited at the surface and bulk in a gradient pattern, with decreasing deposition towards the posterior surface.

Conclusions:
A novel model to demonstrate asymmetric uptake of lysozyme by different CL materials has been developed. The location of lysozyme in the bulk and on the surface varied across different FDA CL groups. It is well established that etafilcon A CLs exhibit high levels of lysozyme, and this study demonstrates that it is present throughout the material and most of it is located in the bulk.